men acquainted with the trees and shrubs which will endure the climate of the country. Works upon jurisprudence have been written by Macieiowski, Budny and Sanwicki. The present university of Warsaw arose from the law school founded by count Lubieuski. With respect to the historical literature of Poland, we refer particularly to the Revue Encyclopédique (Oct., 1827).

POLAR BEAR. (See Bear.) POLAR EXPEDITIONS. (See North Pole, Expeditions to.)

POLARITY. (See Electricity, and Magnetism.)

POLARIZATION OF LIGHT; a new branch of optical science, that has sprung from an observation of Malus, who noticed that when a beam of light is reflected from the surface of a transparent body, at a certain angle, it acquires the same singular property which is impressed upon it in the act of double refraction. (See Refraction, Double.) If a solar ray fall on the anterior surface of an unsilvered mirror plate, making an angle with it of 35° 25', the ray will be reflected in a right line, so that the angle of reflection will be equal to the angle of incidence. If, in any point of its reflected path, we receive it on another plane of similar glass, it will suffer, in general, a second general reflection. But this reflection will vanish, if the second plate of glass form an angle of 35° 25′ with the first reflected ray, and at the same time be turned so that the second reflection is made in a plane perpendicular to that in which the first reflection takes place. For the sake of illustration, suppose that the plane of incidence of the ray on the first glass, coincides with the plane of the meridian, and that the reflected ray is vertical: then, if we make the second inclined plate revolve, it will turn round the reflected ray, forming always with it the same angle; and the plane in which the second reflection takes place will necessarily be directed towards the different points of the horizon in different azimuths. This being arranged, the following phenomena will be observed:-When the second plane of reflection is directed in the meridian, and consequently coincides with the first, the intensity of the light reflected by the second glass is at its maximum: in proportion as the second plane, in its revolution, deviates from its parallelisin with the first, the intensity of the reflected light will diminish; finally, when the second plane of reflection is placed in the prime vertical, that is, east

and west, and consequently perpendicular to the first, the intensity of the reflection of light is absolutely null on the two surfaces of the second glass, and the ray is entirely transmitted. Preserving the second plate at the same inclination to the horizon, if we continue to make it 'revolve beyond the quadrant now described, the phenomena will be reproduced in the inverse order; that is, the intensity of light will increase precisely as it diminished, and it will become equal at equal distances from east and west. Hence, when the second plane of reflection returns once more to the meridian, a second maximum of intensity, equal to the first, recurs. From these experiments it appears, that the ray reflected by the first glass is not reflected by the second, under this incidence, when it is presented to it by its east and west sides; but that it is reflected, at least in part, when it is presented to the glass, by any two others of its opposite sides. Now, if we regard the ray as an infinitely rapid succession of a series of luminous particles, the faces of the ray are merely the successive faces of these particles. We must hence conclude that these particles possess faces endowed with different physical properties, and that, in the present circumstance, the first reflection has turned towards the same sides of space similar faces, or faces equally endowed, at least, with the property under consideration. It is this arrangement of its molecules which is called the polarization of light, assimilating the effect of the first glass to that of a magnetic bar, which would turn a series of magnetic needles all in the same direction. Similar phenomena may be produced, by substituting for the mirror glasses polished plates, formed, for the greater part, of transparent bodies. The two planes of reflection must always remain rectangular, but they must be presented to the luminous ray at different angles, according to their nature. Generally, all polished surfaces have the property of thus polarizing light, more or less completely; but there is for each of them a particular incidence in which the polarization that it impresses is most complete. When a ray of light has received polarization in a certain direction, by the process just described, it carries with it this property into space, preserving it without perceptible alteration, when we make it traverse perpendicularly a considerable mass of air, water, or any substance possessed of single refraction. But the sub

stances which possess double refraction, in general, alter the polarization of light, and apparently in a sudden manner, communicating to the polarized ray a new polarization of the same nature, but in another direction. Among the most interesting phenomena connected with this subject, are the colors produced by the action of crystallized bodies upon polarized light. When thin plates of glass, selenite, mica, agate, quartz-crystal, tourmaline, &c., are exposed in a beam of polarized light, the most beautiful and vivid colors, resembling those observed by Newton in thin films of air or liquids, only infinitely more striking, make their appearance. The attentive examination of these colors has led to a theory both of polarization and double refraction, which, says Herschel, in his Discourse on the Study of Natural Philosophy, is so happy in its adaptation to facts, and in the coincidence with experience of results deduced from it by the most intricate analysis, that it is difficult to conceive it unfounded. Our limits do not permit us to go farther into this interesting subject; for a more complete elucidation of which, we must refer the reader to the article Polarization of Light, in the Library of Useful Knowledge.

POLE, Reginald, cardinal, an eminent statesman and ecclesiastic, born in 1500, was the son of sir Richard Pole, lord Montacute, cousin to Henry VII, by Margaret, daughter of the duke of Clarence, brother to Edward IV. He entered into deacon's orders at an early age, and had several benefices conferred on him by Henry VIII, with whom he was a great favorite. In 1519, he visited Italy, and returned to England in 1525, but, in consequence of the affair of the divorce from Catharine of Arragon, withdrew to Paris. Henry desired to obtain the concurrence of his kinsman in that measure; but Pole, imbued with the maxims of the church of Rome, drew up a treatise De Unitate Ecclesiastica, in which he excited the emperor Charles V to revenge the injury of his aunt. The consequence of this conduct was the loss of all his preferment in England, in return for which, he endeavored to form a party against Henry, which design terminated in the destruction of his brother, lord Montacute, and of his aged mother, then countess of Salisbury, whom the vindictive Henry sent to the scaffold. But the countenance of the court of Rome was extended to Pole, and, besides being raised to the dignity of cardinal, he

was employed in various negotiations. He was also appointed one of the three papal legates to the council of Trent. On the accession of Mary I, his attainder was reversed, and he was invited to England, where he endeavored to moderate the rigor of Gardiner and others against the reformers, and was an advocate for lenient measures, and such a correction of clerical abuses as would conciliate them. On the death of Cranmer, Pole, then, for the first time, ordained priest, became archbishop of Canterbury, and was, at the same time, elected chancellor of both the universities; and, while he acted with much severity in the extirpation of heresy, he made several salutary regulations for the advancement of learning. He died in 1558. Cardinal Pole seems not to have been a man of commanding talents, either political or literary; but he merited great esteem for his mildness, generosity, and comparative moderation, in an age when persecution was deemed lawful on all sides.

POLE, in magnetism. Two points of a loadstone, corresponding to the poles of the equator, the one pointing to the north, the other to the south, are called poles. (See Magnetism.)

POLE OF POLAR STAR is a star of the second magnitude, the last in the tail of Ursa Minor.

POLE, PERCH, or Ron, in surveying, is a measure containing sixteen feet and a half.

POLE-AXE; a sort of hatchet nearly resembling a battle-axe, having a handle about fifteen inches long, and being furnished with a sharp point, bending downwards from the back of its head. It is principally used on board of ships, to cut away the rigging of an adversary who endeavors to board. They have also been sometimes employed in boarding an enemy whose hull was more lofty than that of the boarders, by driving the points into her side, one above another, and thereby forming a kind of scaling-ladder; whence they are sometimes called boarding-ares.

POLES OF THE ECLIPTIC; two points on the surface of the sphere, 23° 30′ distant from the poles of the equator, and 90° distant from every part of the ecliptic.

POLEMBURG. (See Poelemburg.)

POLENDA, or POLENTA; a national dish in Italy, particularly in the northern part of the country, but very common in all the Mediterranean seaports. It is a kind of soft pudding made of the flour of chestnuts or maize, generally with small pieces of meat in it.

Prussia declared that the secret police-a necessary evil in times such as had just terminated-was abolished for the future. Whether it actually was abolished for a moment, we do not know; but we know that it existed not long after, and flourishes at present in that country, as in all other important governments on the European continent. One duty of the secret police always is to open suspected letters; and this was done even under Louis XIV. The more absolute a government is, and the more it strives to be the sole moving and regulating principle of the society, to the destruction of individual freedom, the more will the police be developed; whilst, on the other hand, the freer a country is, and the more it follows the principle, that every thing which can be possibly left to take care of itself, should be so left, the more strictly is the police confined to mere matters of municipal regulation. The scientific spirit of the Germans, connected with the character of their governments, has given rise, in that country, to the police sciences, so called, which are systematically developed and thoroughly cultivated. It is true, that, from the arbitrary nature of the governments, this branch of administration is extended to many subjects which, in freer states, would be left to general law or individual discretion; but, as it is obviously much easier to perfect some branches of the police in absolute governments than in free countries, particularly the medical police, valuable hints may be derived from the German system. In no country has the medical police been so much developed (frequently, it is true, to the annoyance of the people) as in Prussia, because no country ever combined more scientific men with an absolute government. Without, then, taking the Prussian medical police as a model in every particular, it has many points which it would be wise in other nations to imitate. In free countries, the place of a secret police is, in a great measure, supplied by public opinion and the liberty of the press; and it is curious to observe how the most secret transactions, or correspondence, will by degrees come to light; in fact, in some free countries, a politician needs to be quite as much on his guard against making statements in writing, as in absolute governments, since the danger of their reaching the press is as great as that of their detection by a secret police. The first police regulations are met with in Egypt. (q. v.) The Mosaic code, partly founded on the Egyptian, contains many rules of this sort. The police of the

Greeks was excellent. With them, as with their imitators the Romans, the police formed a separate branch of the administration. The capitularies of the Frankish kings contain the next police regulations. In 1548 and 1577, the German empire became subject to such regulations. Some account of the police of London is contained in the article London. The king of England, in his speech from the throne in the winter of 1831, recommends an improvement of the police of the kingdom. (See Politics.)

POLICINELLO. (See Punchinello.)

POLICY OF INSURANCE. (See Insurance.) POLIGNAC, Melchior de, abbé, and subsequently cardinal, a French diplomatist, born 1661, died 1741, was descended from a distinguished family of Languedoc. In 1689, he rendered himself conspicuous by his address in the negotiations with pope Alexander VIII, relative to the articles adopted by the French clergy in 1682. In 1693, the abbé de Polignac was named ambassador extraordinary to Poland, for the purpose of detaching John Sobieski from the league with Austria, and drawing him over to an alliance with France. On the death of Sobieski (1696), he was employed in endeavoring to effect the election of the prince of Conti to the Polish throne. His intrigues, though seconded by large bribes, were, however, unsuccessful. On his return to France, in 1698, he was banished the court on account of the failure of this mission. In 1710, he was sent to take part in the negotiations at Gertruydenberg, and, in 1712, was appointed plenipotentiary to the congress of Utrecht, and was afterwards minister to the court of Rome. As a writer, Polignac is known by his didactic poem, in eight books, against the Epicurean system, entitled Anti-Lucretius, seu de Deo et Natura (Paris, 1747), which has been translated into English, French and German. He died in 1741. (See the Histoire du Cardinal de Polignac.)

POLIGNAC, Auguste Jules Armand Marie, prince de, ex-minister of France, was born in 1780. His mother, the favorite of Marie Antoinette, and governess in the royal family, was married, in 1767, to the count de Polignac, who was descended from the same illustrious family as the cardinal. (See the preceding article.) In 1780, her husband was created duke, and, soon after, the duchess became governess to the young dauphin. In 1789, in consequence of some manifestations of popular hatred, she and her husband left France, with the count d'Artois (since Charles X),